Recently, demand for a surveillance camera is increasing with the purpose of crime prevention, field supervision and the like. Further, the function of the surveillance camera is diversifying with the development of semiconductor technology and network technology.
The surveillance camera is easily affected by the change of atmosphere and lighting, and thus improving visibility of an image from the influence is one of the important tasks in the surveillance camera. Among such tasks, an image correction technique represented by stabilizer correction, gradation correction, external disturbance (fog, rain, snowstorm, yellow dust, smog and the like) correction and the like is important and has been applied to various products until now.
A heat haze is one of the natural phenomena that degrade the image visibility of the surveillance camera. When atmospheres having different densities are locally mixed with each other due to the temperature difference of an air and the like, light is refracted to generate a heat haze. If the heat haze is generated, a deformed object is observed. Therefore, in reproduction of a taken image, particular regions in the image appear to fluctuate greatly. As such, the distortion caused by an air fluctuation phenomenon due to a heat haze and the like occurs in the image. For this reason, the visibility of an object is degraded.
In Patent Document 1, it is determined whether or not distortion in an image caused by air fluctuations (in this specification, hereinafter, simply referred to as “distortion”) occurs. If it is determined that the distortion occurs, a plurality of images is generated by a continuous shooting and the images are added (averaged) to create one image in which the distortion has been corrected.
In Patent Document 2, an image correction of a heat haze and the like is performed based on an image before one frame.
[Patent Document 1] Japanese Patent Application Publication No. 2012-182625
[Patent Document 2] Japanese Patent Application Publication No. 2011-229030
As in the Patent Documents 1 and 2 above-described, if a plurality of past images taken by continuous shooting are added (averaged), in a case where a moving object (a moving subject) is included in the images, the moving object is projected doubly or trebly. Therefore, there is a possibility that the images are greatly degraded.